Hypofractionated stereotactic body radiotherapy for localized prostate cancer - first Nordic clinical experience

The use of hypofractionated stereotactic body radiotherapy (SBRT) as primary treatment modality in clinically localized prostate cancer (PCa) is emerging, because the low α/β-ratio favors the use of high dose per fraction in PCa. There is a need for more data about SBRT, especially in high-risk PCa patients. The purpose of this retrospective study was to evaluate the safety and the short-term efficacy of robotic SBRT in a clinical patient cohort with localized PCa including also high-risk patients (D'Amico risk stratification).

A total of 240 consecutive patients with clinically localized PCa were treated primarily with SBRT to total doses of 35 Gy or 36.25 Gy in 5 fractions using a robotic SBRT device (CyberKnife^®). All risk groups (D'Amico risk stratification) were represented as follows: 48 (22%), 59 (27%) and 111 (51%) of the patients representing low-, intermediate- and high-risk group, respectively. Data on acute and intermediate-term toxicities and early PSA responses were analyzed.

Neither acute grade 3 or higher GU nor rectal toxicity was observed. Regardless of the fact that 29 (13.3%) patients experienced intermediate-term toxicity requiring diagnostic interventions, the rates of intermediate-term grade 3 GU, rectal and infectious toxicity were low, 1.8%, 0.9% and 1.4%, respectively. A biochemical relapse was observed in ten (4.6%) patients. With the median follow-up time of 23 months the biochemical relapse-free survival (bRFS) rate was 100%, 96.6% and 92.8% in low-, intermediate- and high-risk group, respectively.

The toxicity of robotic SBRT in a large clinical cohort of PCa patients was tolerable and the early PSA response was good in all risk groups. The hypofractionated SBRT offers a possibility to high dose per fraction and to provide the whole radiotherapy treatment within two to three weeks.